A first type of conventional vibration-isolating unit of ten used in constructions is shown in FIG. 1 and usually referred to as a laminated-rubber bearing unit. This type of vibration-isolating unit is produced by alternately disposing a plurality of metal sheets 13 and rubber laminae 14 between an upper bearing plate 11 and a lower bearing plate 15 to form a module, and subjecting the module to high pressure and curing, so that inner binding surfaces of the upper and the lower bearing plate 11, 15 are closely bound to a rubber outer wall 12 to form an integral body. The completed laminated-rubber bearing unit is in the form of a solid rubber cylinder providing a high bearing force. The upper and the lower bearing plate 11, 15 are pre-formed along their outer peripheries with a plurality of bolt mounting holes 16 for fixing the unit to and between the foundation and the column of the construction with bolts.
FIG. 2 shows a second type of conventional vibration-isolating unit that is usually referred to as a lead-cored laminated-rubber bearing unit, which is structurally and functionally similar to the laminated-rubber bearing unit of FIG. 1, except that it includes a lead cylinder 17 forming a core of the laminated-rubber bearing unit for the same to have upgraded vertical bearing capacity and deformation absorbing capacity.
The first and the second type of vibration-isolating units are functionally similar to each other. They all employ a laminated body formed from alternately disposed rubber laminae 14 and metal sheets 13 as a load-bearing elastomer. The upper and the lower bearing plate 11, 15 are separately located at two ends of a secant plane on a column of the construction. When the construction is subject to earthquake energy that results in vertical loading and displacements 19 of the construction, the laminated body formed from the rubber laminae 14 is changed into a barrel-like configuration or has a horizontal displacement and stretch 20, depending on its stress direction, to absorb the earthquake energy by taking advantage of an elasticity of rubber material.
When the above-mentioned vibration-isolating units are newly produced, they usually provide pretty good bonding capacity and restoring force to bear a high magnitude of displacement and stretch 20. However, these rubber-made vibration-isolating units are subjected to a shortened life due to many factors, including long-term ultra-high load and compression that results in structural changes and deformation of the rubber material, environmental climate, as well as temperature and humidity at the mounting location. When the vibration-isolating units have been used for a prolonged time, the bonding capacity of upper and the lower bearing plate 11, 15 to the laminated rubber body tends to reduce, and the units gradually lose their restoring force to bear the high magnitude of displacement and stretch 20. The cylindrical lead core 17 is initially provided for an upgraded capacity of absorbing deformation caused by vertical loading and displacement 19 and has a high plasticity as a preferred advantage thereof. However, the lead core 17 might have become seriously distorted and deformed under long-term compression by the ultra-high weight of the construction and different displacement angles resulted from earthquake origins from different directions. That is, the lead core 17 might have become extended, distorted, shortened, expanded, or even has a deformed shape 21 to separate from the laminated rubber body 14 and form gaps 18 between them, and could no longer be fitly and stably positioned in the laminated rubber body to produce its expected effect.
FIGS. 4 and 5 are perspective and side sectional views, respectively, of a third type of conventional vibration-isolating unit in the form of damper made of reinforced steel plates. This third type of vibration-isolating unit is produced by means of cutting thick steel plates into intermediate bearing plates 23 having a predetermined shape. The similarly shaped intermediate bearing plates 23 are equally spaced in the same direction, and are connected at upper and lower ends to even thicker upper and lower bearing plates 22, 24, respectively, by way of full fillet weld 25. The damper formed by densely welding so many similarly shaped steel plates of the same material to an extended plane would have a quality easily affected by temperature, time, operator's skill and workmanship, and changes in the stress of the steel material. It is therefore doubtful whether the damper of FIG. 4 having a stiff structural design is able to absorb vibrations from all directions. Moreover, this type of damper must be mounted along with large-scaled H-beam steel onto sidewalls of the construction in a predetermined pattern, and therefore requires complicate mounting procedures. In addition, it is uneasy to have good finishing at joints of the dampers with the sidewalls of the construction.
The above-described conventional vibration-isolating units for constructions are generally functionally reinforcing products. There are not commercially available all-directional earthquake-resisting products adapted to moderately dissipate or absorb the very strong instantaneous earthquake energy.
The above-described conventional vibration-isolating units all include a solid cylinder or a plurality of solid plates connected to upper and lower bearing plates to provide pretty good bearing capacity in terms of earthquake energy in a vertical direction. These solid cylinder or plates are, however, restricted by the upper and lower bearing plates to have inferior absorption efficiency in terms of horizontal displacement caused by earthquake energy in a horizontal direction.
Moreover, these conventional units are designed in an attempt to directly resist the earthquake energy with the hardness of their stiff structures. Such a design is obviously improper and not suitable for use below the foundation of a long-lived construction in view that no material has a hardness or strength high enough to directly resist the earthquake.